This patent specification relates to medical ultrasound imaging systems. In particular, it relates to a method and system for enhanced ultrasonic viewing of a specular instrument such as a biopsy needle inserted into the body during a medical procedure.
Ultrasound imaging systems are being increasingly used in medical diagnosis, surgery, and treatment because they are non-invasive, easy to use, capable of real-time operation, and do not subject patients to the dangers of electromagnetic radiation. Instead of electromagnetic radiation, an ultrasound imaging system transmits sound waves of very high frequency (e.g., 1 MHz to 15 MHz) into the patient and processes echoes scattered from structures in the patient""s body to derive and display information relating to these structures.
Among the many practical applications of ultrasound imaging systems is their use during invasive or partially invasive medical procedures for allowing the medical professional to better visualize and control the procedure. For example, a breast biopsy is a medical procedure in which a specialized biopsy needle is inserted into the breast to extract tissue samples of a suspicious lesion or tumor. The biopsy needle must be accurately guided so that its tip enters the lesion. Using an ultrasound imaging system, the physician or other medical professional (hereinafter xe2x80x9cuserxe2x80x9d) can guide the biopsy needle by viewing real-time ultrasound images of the biopsy needle with respect to the target lesion.
A problem, however, arises in practical clinical applications as a result of the thin, specular nature of most biopsy needles. Because they are elongated and narrow, biopsy needles often elude the plane of the ultrasound slice being imaged. When they do intersect this plane, it is often for only brief intervals of time or space.
Another problem arises from the smooth, metallic nature of most biopsy needles. These needles are specular reflectors that, unlike the tissues in the patient""s body, do not reflect incident ultrasound pulses in a diffuse manner. This makes the biopsy needle difficult to perceive in the ultrasound output image unless the incident ultrasound pulses approach the biopsy needle at angles close to ninety degrees. Only for those angles close to ninety degrees will the incident pulses be reflected back to the probe transducer array and properly detected. This problem is alleviated somewhat for abdominal procedures (e.g. for heart, liver, and prenatal procedures) that predominantly use curvilinear imaging formats. For curvilinear imaging formats, the scan lines spread out over a substantial ranges of angles, some of which are perpendicular, or close to perpendicular, to the biopsy needle. In contrast, the predominant imaging format for breast biopsy procedures is the linear format, in which the scan lines are generally parallel to each other, thereby making biopsy needle visualization more difficult for many angles. Nevertheless, it is to be appreciated that the preferred embodiments described infra may be used to enhance needle visualization for any type of imaging format, including linear formats, steered linear formats, curvilinear formats, sector formats, vector formats, and other formats.
U.S. Pat. No. 6,048,312 (hereinafter xe2x80x9cthe ""312 patentxe2x80x9d), which is incorporated by reference herein, discusses a method for three-dimensional ultrasound imaging of a needle-like instrument, such as a biopsy needle, in which the transmitted ultrasound beams are steered to increase the angle at which they impinge upon the biopsy needle. This increases the system""s sensitivity to the needle because the reflections from the needle are directed closer to the transducer array. The steered image frames, i.e., the image frames formed from the steered ultrasound beams, may be superimposed with non-steered image frames to form a composite image, and the needle may be highlighted using an intensity-mapping procedure. When the position of the biopsy needle is undetermined, a non-steered first image frame may be combined with a second image frame acquired by steering the beam at a constant first steering angle and with a third image frame acquired by steering the beam at a constant second steering angle, to increase visibility of the biopsy needle.
However, the ""312 patent leaves several problems associated with biopsy needle imaging unresolved. For example, while the beams are steered by a transmitter and receiver that xe2x80x9care operated under control of a host computer or master controller [ ] responsive to commands by a human operator,xe2x80x9d (col. 5, lines 63-65), the nature of the system""s determination of the biopsy needle position is not clear. As another example, the acquired 2-D ultrasound slices have reduced visibility of the biopsy needle when it is positioned out-of-plane with respect to the ultrasound slice. As described supra, this problem is caused by the elongated, narrow shape of the biopsy needed. This problem can be at least partially remedied by a method disclosed in the ""312 patent, a xe2x80x9ccut plane rotatexe2x80x9d method, in which the user graphically manipulates a slice within a 3-D volume construction of the target region until the biopsy needle is coplanar with the slice, wherein data from the 3D volume corresponding to the slice is then displayed (col. 11, lines 18-44). However, this process is highly computationally intensive, and may therefore be difficult to achieve in a real-time system in a cost-effective manner. Moreover, this procedure demands a substantial amount of user attention and manipulation of the ultrasound user interface. Often, the user is already highly occupied with the biopsy procedure being performed, and does not want to devote an undue amount of time and attention to a system that is supposed to be making things easier.
Accordingly, it would be desirable to provide an ultrasound system with real-time biopsy needle visualization enhancement for a wide range of needle positions with respect to the probe.
It would be further desirable to provide such an ultrasound system in which biopsy needle visualization may be enhanced when the needle position is not predetermined or provided to the system by the user.
It would be further desirable to provide such an ultrasound system having an optional mode in which estimates of the position of the biopsy needle may be easily provided by the user, the ultrasound system having an intuitive, easy-to-use user interface that does not require excessive user manipulation.
It would be even further desirable to provide such an ultrasound system in which biopsy needle visualization may be enhanced even when the biopsy needle may wander or deviate from the plane of the ultrasound slice being imaged.
It would be still further desirable to provide such an ultrasound system that provides such biopsy needle visualization enhancement without requiring the computational intensity associated with 3-D volume construction.
A method and system for real-time visualization enhancement of a biopsy needle are provided, wherein a wide range of needle positions with respect to the probe axis and with respect to the imaged plane are accommodated. Ordinary ultrasound frames are compounded with special purpose ultrasound frames and then output to a real-time display, the special purpose ultrasound frames having transmit and receive parameters adapted to highlight reception of ultrasound echoes from the biopsy needle. In one preferred embodiment, an elevation beam width associated with the special purpose ultrasound frames is wider than an elevation beam width associated with the ordinary ultrasound frames. This reduces sensitivity to the position of the biopsy needle with respect to the imaged plane, and increases reception of biopsy needle echoes in cases where the biopsy needle deviates from the imaged plane. Methods for increasing the elevation beam width of the special purpose frames include lowering the operating frequency and managing the elevation aperture.
Preferably, the beams of the special purpose ultrasound frames are steered such that they are incident upon the biopsy needle at an increased angle as compared to the angle of incidence for ordinary ultrasound frames. For cases in which both the biopsy needle depth and the biopsy needle angle are known, each scan line of the special purpose ultrasound frames has an independently-assigned lateral focus depth equal to a distance between the transducer array and the biopsy needle along that scan line. The biopsy needle image is improved because each point on the needle is in focus with respect to the lateral dimension of the ultrasound image. Edge enhancement, noise/clutter suppression, thresholding, segmentation, or other image processing algorithms may be performed on the special purpose frames prior to compounding. Lesion-enhancement algorithms may also be applied to the special purpose frames and/or to the ordinary frames, wherein both the target lesion and the biopsy needle appear highlighted on the user display.
Processing time for the special purpose frames may be reduced, and therefore overall frame rate increased, by reducing the number of scan lines in the special purpose frame. Because the biopsy needle shape is predictably straight, it has been found that needle image quality does not appreciably deteriorate even when the number of scan lines is decreased by 50 percent or more from the number of scan lines in the ordinary image. Furthermore, several of the image processing algorithms performed on the special purpose frames, including edge enhancement and noise/clutter suppression, may be one-dimensional in nature and separately applied to the scan lines for further reducing processing time.
Values for the needle depth and orientation may be fixed to a known value (e.g., where a fixed mechanical needle guide is used), may be provided by a position sensing system, may be provided by the user, or may be automatically and dynamically determined in accordance with a preferred embodiment described herein. According to a preferred embodiment, a fast method for automatically determining the depth and orientation of a biopsy needle is provided, wherein an exploratory beam is swept across the target region, at periodic or non-periodic intervals, across a wide range of angles. Echoes from the exploratory beam are then processed in a substantially one-dimensional algorithm, or optionally in a two-dimensional algorithm, to determine the depth and orientation of the biopsy needle. The ultrasound beams for the special purpose frames may then be steered to the computed orientation and laterally focused according to the computed depth. The ultrasound system thereby automatically adapts to the position of the biopsy needle for providing enhanced visualization thereof.
According to another preferred embodiment, a simplified method and user interface therefor are provided for enhancing biopsy needle visualization, in which respective special purpose frames are steered at a plurality of predetermined angles, wherein the special purpose frames are compounded with ordinary frames and output to a display. In one preferred embodiment, only a few angles (e.g., +30 degrees and xe2x88x9230 degrees) are taken for the special purpose frames. In another preferred embodiment, a plurality of angles are used, the number of angles being not less than a quotient of a maximum field angle divided by a critical separation angle. It has been found that this critical separation angle is typically between about 10 to 16 degrees. In one embodiment, a single toggle button is provided to the user that activates a needle enhancement mode and selects the number of steering angles to be used. In another preferred embodiment, a plurality of toggled selection buttons is presented to the user in a spatial pattern that emulates predetermined ranges of needle angles, whereby the user may intuitively select the number and direction of steering angles to be used for the special purpose frames.